ACTG 317: The purpose of this study is to determine if there are differences between men and women in how zidovudine (ZDV) is taken into the body, used by the body, and removed from the body. For women, the study will also look at whether or not taking birth control pills or a birth control injection influences the way the body takes in, makes available, and removes ZDV. The study will also try to determine if birth control pills or injections change the level of HIV in the blood or genital tract.